1. Field of the Invention
The present invention relates to downhole tools. More particularly, the invention relates to the control of downhole tools in a drill string from the surface of a well.
2. Description of the Related Art
Communication to and from downhole tools and components during drilling permits real time monitoring and controlling of variables associated with the tools. In some instances pulses are sent and received at the surface of a well and travel between the surface and downhole components. In other instances, the pulses are created by a component in a drill string, like measuring-while-drilling (“MWD”) equipment. MWD systems are typically housed in a drill collar at the lower end of the drill string. In addition to being used to detect formation data, such as resistivity, porosity, and gamma radiation, all of which are useful to the driller in determining the type of formation that surrounds the borehole, MWD tools are also useful in transmitting and receiving signals from the other downhole tools. Present MWD systems typically employ sensors or transducers which continuously or intermittently gather information during drilling and transmit the information to surface detectors by some form of telemetry, most typically a mud pulse system. The mud pulse system creates acoustic signals in drilling mud that is circulated through the drill string during drilling operations. The information acquired by the MWD sensors is transmitted by suitably timing the formation of pressure pulses in the mud stream. The pressure pulses are received at the surface by pressure transducers which convert the acoustic signals to electrical pulses which are then decoded by a computer.
There are problems associated with the use of MWD tools, primarily related to their capacity for transmitting information. For example, MWD tools typically require drilling fluid flow rates of up to 250 gallons per minute to generate pulses adequate to transmit data to the surface of the well. Additionally, the amount of data transferable in time using a MWD is limited. For example, about 8 bits of information per second is typical of a mud pulse device. Also, mud pulse systems used by an MWD device are ineffective in compressible fluids, like those used in underbalanced drilling.
Wireline control of downhole components provides adequate data transmission of 1,200 bits per second but includes a separate conductor that can obstruct the wellbore and can be damaged by the insertion and removal of tools.
Other forms of communicating information in a drilling environment include wired assemblies wherein a conductor capable of transmitting information runs the length of the drill string and connects components in a drill string to the surface of the well and to each other. The advantage of these “wired pipe” arrangements is a higher capacity for passing information in a shorter time than what is available with a mud pulse system. For example, early prototype wired arrangements have carried 28,000 bits of information per second.
One problem arising with the use of wired pipe is transferring signals between sequential joints of drill string. This problem has been addressed with couplings having an inductive means to transmit data to an adjacent component. In one example, an electrical coil is positioned near each end of each component. When two components are brought together, the coil in one end of the first is brought into close proximity with the coil in one end of the second. Thereafter, a carrier signal in the form of an alternating current in either segment produces a changing electromagnetic field, thereby transmitting the signal to the second segment.
More recently, sealing arrangements between tubulars provide a metal to metal conductive contact between the joints. In one such system, for example, electrically conductive coils are positioned within ferrite troughs in each end of the drill pipes. The coils are connected by a sheathed coaxial cable. When a varying current is applied to one coil, a varying magnetic field is produced and captured in the ferrite trough and induces a similar field in an adjacent trough of a connected pipe. The coupling field thus produced has sufficient energy to deliver an electrical signal along the coaxial cable to the next coil, across the next joint, and so on along multiple lengths of drill pipe. Amplifying electronics are provided in subs that are positioned periodically along the string in order to restore and boost the signal and send it to the surface or to subsurface sensors and other equipment as required. Using this type of wired pipe, components can be powered from the surface of the well via the pipe.
Despite the variety of means for transmitting data up and down a string of components, there are some components that are especially challenging for use with wired pipe. These tools include those having relative motion between internal parts, especially axial and rotational motion resulting in a change in the overall length of the tool or a relative change in the position of the parts with respect to one another. For example, the relative motion between an inner mandrel and an outer housings of jars, slingers, and bumper subs can create a problem in signal transmission, especially when a conductor runs the length of the tool. This problem can apply to any type of tool that has inner and outer bodies that move relative to one another in an axial direction.
Drilling jars have long been known in the field of well drilling equipment. A drilling jar is a tool employed when either drilling or production equipment has become stuck to such a degree that it cannot be readily dislodged from the wellbore. The drilling jar is normally placed in the pipe string in the region of the stuck object and allows an operator at the surface to deliver a series of impact blows to the drill string by manipulation of the drill string. Hopefully, these impact blows to the drill string dislodge the stuck object and permit continued operation.
Drilling jars contain a sliding joint which allows relative axial movement between an inner mandrel and an outer housing without allowing rotational movement. The mandrel typically has a hammer formed thereon, while the housing includes a shoulder positioned adjacent to the mandrel hammer. By sliding the hammer and shoulder together at high velocity, a very substantial impact is transmitted to the stuck drill string, which is often sufficient to jar the drill string free.
Often, the drilling jar is employed as a part of a bottom hole assembly during the normal course of drilling. That is, the drilling jar is not added to the drill string once the tool has become stuck, but is used as a part of the string throughout the normal course of drilling the well. In the event that the tool becomes stuck in the wellbore, the drilling jar is present and ready for use to dislodge the tool. A typical drilling jar is described in U.S. Pat. No. 5,086,853 incorporated herein by reference in its entirety.
An example of a mechanically tripped hydraulic jar is shown in FIG. 1. The jar 100 includes a housing 105 and a central mandrel 110 having an internal bore. The mandrel moves axially in relation to the housing and the mandrel is threadedly attached to the drill string above (not shown) at a threaded joint 115. At a predetermined time measured by the flow of fluid through an orifice (not shown) in the tool 100, potential force applied to the mandrel from the surface is released and a hammer 120 formed on the mandrel 110 strikes a shoulder 125 creating a jarring effect on the housing 105 and the drill string therebelow (not shown) that is connected to the housing at a threaded connection 130.
Methods to run a wire through a jar or tool of this type have not been addressed historically because the technology to send and receive high-speed data down a wellbore did not exist. Similarly, the option of using data and power in a drill string to change operational aspects of a jar have not been considered.
With recent advances in technology like wired pipe, there is a need to wire a jar in a drill string to permit data to continue down the wellbore. There is an additional need for a jar that can be remotely operated using data transmitted by wired pipe, whereby performance of the jar can be improved. There is a further need therefore, for a simple and efficient way to transmit data from an upper to a lower end of a wellbore component like a jar. There is a further need to transmit data through a jar where no wire actually passes through the jar. There is yet a further need for methods and apparatus to control the operational aspects of a jar in order to compensate and take advantage of dynamic conditions of a wellbore.
Jars are only one type of tool found in a drill string. There are other tools that could benefit from real time adjustment and control but that have not been automated due to the lack of effective and usable technology for transmitting signals and power downhole. Still other tools are currently controlled from the surface but that control can be much improved with the use of the forgoing technology that does not rely upon pulse generated signals. Additionally, most of the drill string tools today that are automated must have their own source of power, like a battery. With wired pipe, the power for these components can also be provided from the surface of the well.